Various sealant compositions have been used in electrical connectors, particularly to protect the electrical connection from heat and moisture. Protection from atmospheric attack is especially important in the telecommunications industry as is a high order of long term electrical insulation.
U.S. Pat. No. 3,410,950 discloses a connector having a sealant system, the disclosure of which is incorporated herein by reference. The preinsulated open U or channel-type connector disclosed therein has one insulating film surrounding the outside of the open U-type ferrule, and a second layer of film covering the inside of the ferrule, the ferrule having one or more wire receiving projections on its inside surface. Sealing material is contained between the inside insulating film and the surface of the ferrule adjoining the projections. When the connector is crimped onto wires, the projections rupture the inside film layer permitting the sealing material to flow around the wires.
Generally the sealants used with connectors of the type described above have a silicone base. Although these sealants do repel moisture, the sealant have tendency over a period of time to creep out of the connector. Their oil base has been observed to separate and to "cream" or bleed during storage. Furthermore, fractions of the silicone based sealants have significant vapor pressure under common ambient conditions. Fractions of the sealant, therefore, vaporize when it is exposed to the atmosphere and condense on nearby surfaces including switch gear contacts resulting in accelerated arcing and corrosion.
The sealant material disclosed herein has equivalent dielectric properties of silicone based sealants. The problems described above, however, are greatly reduced. The composition of the invention is more hydrophobic than silicone based sealants. The sealant has a higher viscosity, thus greater reducing the problem of "creep". The lower vapor pressure of the herein disclosed sealant greatly decreases the problem of contamination of the surrounding area.
The sealant is a homogeneous mixture comprised of a polymeric polyester derived from adipic acid and a fumed silica. The polyester comprises from about 80 percent to about 85 percent by weight of the mixture and the fumed silica comprises from about 15 percent to about 20 percent by weight of the mixture. In the preferred embodiment the mixture is further comprised of from about 0.02 percent to about 0.04 percent of silane to increase the homogeneity and the moisture repellency of the sealant. From about 0.03 percent to 0.07 percent of a low interfacial tension surfactant is also added to increase the wetting and dispersion of the fumed silica.
Antimicrobial agents, corrosion inhibitors and/or antioxidants may also be added to the formulation.
The use of sealants in electric connectors can be understood by referring to the following drawings.